1. Field of the Invention
The present invention relates to the field of OLED (Organic Light-Emitting Diode) manufacture, and in particular to a heating device for vapor deposition of an OLED material.
2. The Related Arts
An OLED (Organic Light-Emitting Diode) is a flat panel displaying technique of extremely prosperous future and it shows excellent displaying performance and also possesses various advantages, such as being self-luminous, simple structure, being ultra-thin, fast response speed, wide view angle, low power consumption, and being capable of achieving flexible displaying and is thus regarded as a “dream display”. In addition, the investment of the manufacturing installation is far less than that of liquid crystal displays so that it has attracted the attention of major display manufacturers and becomes the mainstream of the three-generation display devices of the field of display technology.
An OLED often comprises: a substrate, an ITO (Indium Tin Oxide) transparent anode arranged on the substrate, an organic material layer formed on the ITO transparent anode, and a cathode formed on the organic material layer. The organic material layer is composed of: a hole injection layer (HIL), a hole transport layer (HTL) formed on the hole injection layer, an emissive layer (EML) formed on the hole transport layer, an electron transport layer (ETL) formed on the emissive layer, and an electron injection layer (EIL) formed on the electron transport layer. To increase the efficiency, the emissive layer often adopt a host/guest doping system.
Two operations are generally used to manufacture an OLED organic material film. For high-molecule OLED organic materials, solution based film forming process is used; however, such a process is still in laboratory test stage. For small-molecule OLED organic materials, a vacuum thermal evaporation based film forming process is commonly used currently. Such a process is widely used by most manufacturers of the flat panel display industry, such as Samsung and LG.
Film formation with vacuum thermal evaporation is to heat, in a vacuum environment of less than 5×10−5Pa, a sublimateable or meltable OLED material for changing from a solid state to a vapor state. Gas molecules are moving at a high speed to reach a glass substrate and get deposited, condensed, and solidified on the substrate to form a solid film of the OLED material. As shown in FIG. 1, a conventional heating device that used for deposition of OLED materials comprises a crucible 100 for receiving and containing an OLED material and a set of heating coil 200 set outside the crucible 100. The crucible 100 is provided with a gas release hole 150 in a center of a top thereof. FIG. 2 is a schematic view illustrating an operation process of the set of heating coil 200 and it can be seen from the drawing that an upper portion 210 and a primary portion 230 of the set of heating coil 200 cannot be individually controlled in respect of the temperatures thereof so that the temperatures can only be increased or decreased synchronously. FIG. 3 is a schematic view illustrating an operation process of the conventional heating device that is used for evaporation of an OLED material. Firstly, the set of heating coli 200 is energized and an OLED material 300 disposed inside the heating device starts to raise the temperature. When the temperature is increased to reach the evaporation temperature of OLED material 300, gaseous molecules of the OLED material 300 flows out of the gas release hole 150 to deposit on a substrate. When the OLED material 300 is almost running up for evaporation or when there will be an extended period of idle time of the experiments, the heating device needs to lower down the temperature and power supply to the set of coil 200 is cut off to decrease the overall temperature of the heating device, whereby gas molecules of the OLED material 300 may accumulate and solidify at the gas release hole 150, making the gas release hole 150 jammed, so that the manufacturing process must be interrupted for opening the chamber and processing. This lowers the manufacturing efficiency, increases work load, and also bring potential risk of quality change of the OLED material due to the OLED material being exposed to the atmosphere and thus contacting moisture and oxygen.